An ink-jet recording device ejects ink onto a recording material such as recording paper. A thermal ink-jet system generates bubbles through rapid heating and, as a result of increased pressure, ejects fine ink droplets through fine nozzles. Alternatively, a piezoelectric ink-jet system uses a piezoelectric element to eject fine ink droplets.
Water-based inks are useful in such ink-jet recording devices. Such inks are prepared by dissolving or dispersing various colorants in a liquid medium comprising water and a water-soluble organic solvent. For color printing, the basic colors of water-based ink used are yellow, magenta, cyan and black. In addition to these four colors, light magenta, light cyan, red and green are also often used. In addition to dye inks, pigment inks and particle inks are also used.
The ability to introduce the ink into the ink-jet head is a very important matter for the ink ejection performance and the print quality of the ink-jet recording device. The ability to introduce the ink is influenced by the viscosity, the surface tension, the foaming property and the like of the water-based ink. Even if physical properties such as the viscosity and the surface tension of water-based inks are the same, the ability to introduce the inks into an ink-jet head may differ depending on the composition of the water-based ink and on the type of the colorants in the water-based ink. That is, a water-based ink could have a stable dissolution or dispersion state and therefore could produce good print quality; however, the ability to introduce the ink into an ink-jet head may be poor resulting in problems such as printing failures.
Solutions to such problems have been sought. One method introduces water-based ink into the ink-jet head by introducing a wetting solution into the ink-jet head before shipping. Another method removes the water-based ink and replaces the ink with a wetting solution. This latter method is used when the ink-jet recording devices will not be used for a long time. The water-based ink is reintroduced into the ink-jet head before use (See, for example, U.S. Publication No. 2004/0056918 A1).
However, the relationship between the water-based ink and wetting solution has been unclear in regard to improving the ability to introduce the ink into the ink-jet head. That is, there is no guideline to select the combination of water-based ink and wetting solution.